As already mentioned, within Kruger Park you can stay at the SANP restcamps (use the link provided by Ghalied). They are not expensive, and most of them have a pool, a small shop and a restaurant (dont expect gourmet food). In most of the cabins/tents/bungalows there is a kitchen, and often also a Braai (BBQ) so if you want, you can cook and/or grill yourself.

For self-driving you dont need a 4x4, a normal small sedan does it. Self-driving and looking for animals yourself is a lot of fun and it is very easy to do so within the park. Generally said, the southern part of Kruger is the best for animals, but its also the busiest. With about 6 nights in Kruger NP (which I feel is enough), I would also go for 3 restcamps. Lower Sabie and Satara and maybe Olifants or Skukuza. You definitely want to book the restcamps asap.

I will definitely go to Koh Phangan. I have a friend there. But I'm going after full moon and I will also go to the other side of the island.

All I heard about Lonely Beach was that the "Himmel Bar" plays loud techno music every morning until 5am and every guesthouse in the area is affected by it and people can't sleep. Even now in low season. That's not a "party" but it's definitely too much for me. You don't want to be close to me if I don't get a good night sleep lol

I was told by locals that Koh Kood and Koh Samet are only fun to visit and explore if you have a motorbike. Koh Chang seems to be ok, although some accommodation is more difficult to reach by foot and impossible by public transport.

My first question would be what you plan to do in Nairobi, or even Kenya as a whole. It would be a shame to spend 16 holed up in Nairobi. If you're going to visit Kenya, there's plenty to see and do, but it all depends on your tastes and budget, of course.

You mean you want suggestions for the Ko Chang /Trat coast when you say East Coast, The beaches on Ko Chang tend to disappear at high tide and most have a lot of development . But if beaches such as Lonely Beach and Bangbao or Bai Lan don't appeal then try Long Beach further south although its isolated and harder to get to.
If you want better beaches then head for the next island Ko Kood (Kut) . A bit harder to get to and more time consuming but there is modest priced accomm further behind the beach at Klongchao . One of the nicest beaches is further south at Ao Jark . You may be able to get room for 1000 baht but have limited eating options and the beach is isolated , but you may find the natural beauty makes up for that .

If you decide to stick to your orginal plan of Ko Phangan , then try Thong Nai Pan Noi (stay Sandee Bungalow) or Bottle Beach or Than Sadet.

Why is it gruelling?

If you don't care where you go,you can go anywhere!

Just open an atlas at a random page.Or spin a globe and stop it with your finger....

Lol that's the idea! The problem is finding it within a flight+hotel budget. Essentially, we keep having to change the destination and/or the dates trying to find a place that fits the budget. We're making a list from there, but it's grueling and time consuming having to go through the search process over and over.

August is a great time for the caribe side- hike, kayak, snorkel, beaches, foodie scene.

Since you land at 12, then need to clear Immigration/Customs, its now 1;30...even hiring a taxi direct to La Pavona would be cutting it close for the last boat to Tortuguero...4PM...

I am not sure there is a afternoon flight, check Sansa schedule...

If not head downtown and enjoy some city life around the Mercado Centro and Museums/Cafes.. Stay on edge of this area like Hemingway House, Dunn Inn etc, so its a easy taxi ride the caribe bus terminal. Want to get bus by 8am so you get to Cariarri for the bus connection to La Pavona at 12, boats meet buses to Tortuguero.

Look at staying in the village, not the eco resorts, as they are nice, but isolated and you have to use their boats to get anywhere $$ and eat hotel cafe food...blah blah

Staying in the village is a foot paths and easy to hike the park, get a guide, rent a canoe etc, and then you both food/cafe and lots of lodging options...check Booking.com. I stay at Miss Miriam II....basic and clean, simple, vuew of ocean, close to main drag in town, soccer fields and entrance to hike trails on coast,.

From town main dock arrange boat ride to Moin ( 3 hours). From Moin just taxi hire/share to Cahuita. In Cahuita the best deal on the entire coast is old school thatched roof bunglows at the Alby Lodge, next to town and entrance to park...

From Cahuita (and Limon the port town) buses run every hour in daylight 6AM-5pm) down the coast, so just grab a bus to Pt Viejo, and same applies for buses from PV to Manzanillo.

There are no resorts and big hotels , maybe 6 overall in CR, and there is not anything on the caribe side, other than a new modern 20 room boutique hotel, all 1 floor...see Booking.com

I like to stay in Punta Uva, nice locals beach, PADI shop for dive/snorkel, and beach rentals for boards and boogie boards etc. Playa Chequita and Cocles is great too, small beaches on coves, few people if any.

Rent Bicycles.

For sure raft to San Jose as a day trip from PV. I like this outfit, they have a office on main road going into PV...

https://exploradoresoutdoors.com/tours/pacuare-1-day/

Have fun.